Internal link building involves optimizing the linking structure within a website to improve search engine rankings. A well-structured internal linking system provides context and relevance between pages, guiding users and search engines to important pages. Key strategies include using an information architecture that categorizes pages and links them contextually, implementing breadcrumbs to indicate page hierarchies, and focusing internal link love on "money pages" that are most important for business goals. Done effectively through techniques like Wikipedia-style in-text linking, internal link building can help search engines better understand what pages are most relevant and important within a site.